Jessica Ennis was smiling on the podium, even though she had a silver medal round her neck. She said her grin was because "whenever I get on the podium I think back to Beijing and the Olympics I missed because I was injured". You can see her point but it still seemed a strange way to react to losing the world championship heptathlon title after she had been beaten to gold by the Russian Tatyana Chernova .

Ennis gives little away about how she feels when she appears in public. To get a real insight into her emotions one needed to see her on the start line for the final discipline, the 800 metres. By then she knew she had lost her title and had time to get used to the idea. After her wretched performance in the javelin in the morning she was 133 points behind the 23-year-old Chernova. She would have needed to beat her by more than eight seconds round the two laps of the track to make that up.

As the runners were introduced Ennis ignored the camera and stood, staring down the track with a look of dead-set determination. At that point it was not Beijing 2008 that was on her mind but London 2012. She had a point to prove, to herself and to Chernova. And she did it, running a personal best of 2min 7.81sec.

Her coach, Toni Minichiello, was asked whether Ennis could come back from this. "She already has," he replied. "It would have been very easy for her to take the silver and go home. It wasn't like that. She tried, she put it all on the line and she won't walk away from here thinking 'I wish I'd had a go.'" That 800m told everything about how Ennis is going to react to this defeat – by working harder and getting better. Her team-mate Louise Hazel, who finished 15th, picked up on it too. "Well done to Jess for really making the Russian girl work for it."

The thousands of fans who were lucky enough to get tickets to see Ennis compete next year should not worry. They paid to watch a coronation. Instead they are going to get a fight for the throne. The duel between Ennis and Chernova is going to be one of the most engrossing spectacles of the Olympics. And anyone who wants to write Ennis off now should consider this one statistic: if she had matched her personal best of 46.71m in the javelin, she would have won the gold – by a single point.

Beating Chernova is not going to be easy. Her winning score of 6,880 was 57 points beyond Ennis's personal best. But there are three clear areas where Ennis can pick up points. Her poor performance in the javelin was costly but she also gave away a lot of ground on the first day. She and Chernova have a neat split in their abilities. Ennis is stronger in the first four events but Chernova has an even bigger advantage in the last three.

Ennis produced personal bests in the long jump, the shot and the 800m but by hitting the hurdles on the first morning and underperforming in the high jump she failed to take advantage in the two events in which she normally has the biggest advantage over her new rival. That means there is lots of scope for improvement and that, surely, is what would have been occupying her mind. Ennis said she felt "devastated" when she realised she had lost her title in a tournament she described as "one of the toughest I've had". Can she beat Chernova's 6,880 points? "Yes, definitely I can," she said bluntly. "It's the javelin."

The one real worry about her performance was not her javelin technique but how she responded to the pressure Chernova put on her when she threw 52.95m. Chernova was competing in the first group, Ennis in the second. That meant the 25-year-old from Sheffield had plenty of time to stew on what she had to do. She had thrown more than 45m in practice but seemed to crack when it came to the competition proper. Minichiello made a telling observation when he said he and Ennis would talk to "the psychologists" to pick apart the two days and analyse where she lost. It may simply have been that Ennis had never before taken that kind of blow at that stage of a competition. But she is going to have to get used to it.

As of now, Chernova is the best heptathlete in the world. That should not be a surprise; she has the pedigree. Her father was a decathlete and her mother a 400m runner. She took up athletics as a little girl because she got so bored with sitting around the hotel while the two were out training. Unsurprisingly she was a natural. She won the World Youth Championship in 2005 – breaking the age-group records set by Carolina Kluft – and the World Junior Championships the following year. She was only 20 when she won the bronze in Beijing.

Chernova was asked whether she thought she could beat Jackie Joyner-Kersee's world record of 7,291 points, set at the Seoul Olympics in 1988. "All girls think of breaking the record," the Russian said. "But only one can do it, really."And for the briefest moment, the smile was gone from Ennis's face again, replaced by a slight and fleeting scowl. She and Chernova may have hugged when the heptathlon was all over but the rivalry between these two is going to run all the way to London and probably beyond.